In automotive vehicles, fuel stored in an engine fuel tank may vaporize under certain conditions. Some engine evaporative emissions systems may utilize a carbon canister to collect vaporized fuel from the fuel tank, in order to save fuel and reduce release of fuel vapors to the atmosphere. The vapors stored in the canister are eventually released into the engine intake manifold during operation, a process which may be described as fuel vapor “purging”. In this way, fuel vapors may be recycled to the engine rather than leaked to the environment.
Various approaches for carrying out fuel vapor purging may be used. For example, pressure differentials within the engine may be utilized to draw fuel vapors from the canister into the intake manifold. However, in boosted engines, intake manifold pressure may vary substantially depending on whether the compressor is operating. During vacuum conditions when the compressor is not operating, the intake manifold may have a negative pressure. In contrast, during boost conditions when the compressor is operating, the intake manifold may have a positive pressure. Approaches for fuel vapor purging in boosted engines must be able to carry out the purging during both vacuum conditions and boost conditions.
One system for fuel vapor purging in boosted engines is a dual-path system which utilizes two purge flow paths in order to purge under both vacuum conditions and boost conditions. The system includes a first mechanical check valve between the intake manifold and the canister purge valve (CPV), the first check valve preventing reverse flow through the system during boost conditions. The system further includes a second identical check valve between the CPV and an ejector, to facilitate purging during boost conditions. During non-boost conditions, purge vapors flow through the first check valve before entering the intake manifold. During boost conditions, the ejector is used to generate vacuum for purging. The purge vapors flow through the second check valve, then the ejector, then the compressor, and then a charge air cooler before entering the intake manifold.
However, the inventors herein have recognized that such dual-path systems have several disadvantages. Due to large number of connections and components required, the system may be costly and complex. For example, the system utilizes approximately 11 connections, two check valves, and an ejector. Further, because of the large number of connections, the system may be prone to leakage of vapors. Furthermore, because of the large number of connections and the discrete nature of the components, assembly may be difficult. For example, “plug-and-play” assembly may not be possible.
To address the above issues, the inventors herein have identified various approaches for fuel vapor purging in boosted engines. In one example approach, a method for engine fuel vapor canister purging comprises, during vacuum conditions, purging vapors from the canister into an engine intake passage downstream of a throttle via an ejector. The method further comprises, during boost conditions, purging vapors from the canister into an upstream inlet of a compressor via the ejector, the compressor arranged in the intake passage upstream of the throttle.
In this way, fuel vapor purging may be achieved in a boosted engine using with fewer connections. Whereas a dual-path system may utilize approximately 11 connections, the system described herein may include fewer connections, and thus may be less prone to undesirable fuel vapor leakage. Further, by reducing the number of connections and components, the system described herein may be less costly, and may facilitate assembly. For example, plug-and-play assembly may be possible, thus further reducing costs by simplifying and expediting manufacturing. Finally, the system described herein desirably maximizes vapor flow over the operating range, despite the reduced number of connections. That is, fuel vapor purging may be achieved when operating conditions are such that intake manifold pressure is either less than or greater than atmospheric pressure (e.g., vacuum conditions or boost conditions).
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.